Photographer&#39;s computing device



July 19, 1949. w. M'. FRAzl-:R

PHOTQGRAPHERS COMPUTING DEVICE s sheets-sheet 1 Filed Dec. 4, 1947 1 .5.*76TH M 5252436 (534 3o 32137 60 2 if ,a

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July 19, 1949. w. M. FRAzl-:R 2,476,59

PHOTOGRAPHERS COMPUTING DEVICE Filed Deo. 4, 1947 5 Sheets-Sheet 2 July19, 1949. w. M. FRAZER -PHOTOGRAPI'IERS yCOMPUTING DEVICE 5 Sheets-Sheet3 Filed Dec. 4, 1947 I NV EN TOR. /zz /AM M FeAz-e Patented `uly 19,14949 UNITED STATES APlSi'lTENT OFFICE iT-'GRPE COMPUTING EVIC- Will-iamFreier, Westport, Genn. mineafion eeemier 4, 19:4"7", Serial-iid.is'9,5"s'9 upon shoulder 36 and is retained in position by said head 36.knurled knob 3l which is fixed to plate I4 and facilitates rotatingplate I4. Y n

Ring I2 is divided into portions I2f1L and I2'.J

S6 which isof sufcient diameter to overliea substantial portion of theplate I4 which restsv Surrounding stud head 36 is a 4 48 are in abuttingrelationship stud 64 will be substantially at the left hand end y of thecam groove as viewed in Figure 3, and, when the pointers 46 and 48 arespread widely apart with their enlarged heads 42 and 44 at the outerlimits of the semi-annular space or track I3, where they will beabutting against the oppositel ends of the higher portion I2a of saidring I2, stud 64 will be substantially at the end a of the cam groove.Movement `of the'stud 64'toward the en d y of the cam groove,'caus'esVthe arms vto vmove toward one another and causes stud 64 to moveinwardly in the guide slot 62, and movement of the stud 64 to the end aofthe cam groove 60 will cause stud of differential height. Portion I2aand I2b each comprise approximately 180 of ring I2. Portion I2a ishigher than portion I2b and its top surface is substantially iiush withthe top of plate I4 and the top of ring I6. There is thus provided asemiannular space or track I3 between the outer periphery of plate I4and the inner periphery of ring I6, above the portion I2b of ring I2.Outer ring I6 is stepped on its inner periphery at 38 to receive theradially projecting flange 48 on the higher portion I2a of ring I2 whichthus serves to limit upward displacement of the ring I6.

It willrthus be seen Ythat as illustrated herein, plate I4 and ring I6are rotatable with respect t0 the fixed ring I2,

Received in the semi-annular space or track I3 are the heads 42 and 44of the pointer arms 46and 4S which at their inner ends are pivotallymounted on axial stud I8, around the portion 26 thereof. The pointerheads have a radially projecting portion or flange 4I)94 at their outerends respectively, adapted to overlie and travel on the step 4380i ringI6. The pointer arms 46 and 48 are vc'o-related with plate I4 formovement together as will be explained.`

The ring I6, on its top surface along its inner periphery, is calibratedwith a scale A of the reciprocals of object distances. Plate I4 ismarked on its top surface, around its periphery, with a scale B oflogarithmic calibrations of camera openings.l The higher, substantiallysemi-annular portion I2LL of ring I2 is similarly calibrated on its topsurface, along its yinner periphery, with a scale C of logarithmiccalibrations of lens focal lengths. Y

On the under face of plate I4 a cam groove is cut, the shape of which isdetermined as will be'described. In the upperface of base I0 a guideslot '62 is provided, which, as shown herein, is disposed radially withrespect rto plate I4 Aand its axis I8, and extending between the baseplate and the face plate, with its lower end Vslideably engaged in saidradial slot and its upper end s lideably engaged in said cam slot, is astud 64 whichthus servesas a cam follower. The curvedand oppositelydisposed arms 66 and 68 are rotatablyy Imounted at one end on stud 64and their oth'enends are pivotally connected by pivots 61 and 69 to thepointer arms 46 and 48 respectively, intermediate the ends of saidpointer arms.

Reference to the drawings and particularly to Figure 3 will show thatthe shape of the cam groove 66 is such that when the plate I4 is rotatedthe stud 64 will be forced outwardly in guide slot 62 and this motionwill cause curved arms 66 and 68 to move apart from their abuttingrelationship asshown in Figure 3 and to swing in opposite directions.'Ihe length of the cam ot iss'uch that when the pointer arms 46 and 64to move outwardly inV guide slot 62, in the dif 'rection of thearrow 63.

, A radially extending line of reference 'IIJ may be Vmarked on the to'pof the portion I2b of ring I2, in operative relation to the scale ofobject distances (scale A) on ring I6, and positioned so that when thepointer arms are in abutting relation to one another theirline ofcontact will be coincident with it. Preferably the ring portion ers willbe moved when plate I4 is rotated and vice versa. Thus if plate I4 isrotated to bring a y desired vcamera opening graduation thereon oppositea selected lens Yfocal length graduation on the portion I2ab of ring I2the pointer arms 46 and 48 will be actuated, and contrariwiseif thepointer arms are moved manually, for example, topoint to objectdistances near and far of a given object distance, the plate I4 will berotated thuschanging the position of the camera opening scale (scale B)thereon in relation to the'lens focal length scale (scale C) on the poretion I2EL of the ring I2.

In employing the device disclosed herein the graduation on scale A whichwill be placed opposite the mark, or line of reference 10, on thesurface of ring'portion I2b, and the graduation on scales Band C whichwill be placed opposite one another, will depend on which of the threevariables consisting of lens focal length, size of cameraV opening, anddepth of focus is unknown and to be computed. The practical use of thedevice is illustrated by the following three examples: A

1. If it isdesired to determine which camera opening should be lused toinsure that an object 5 ft. from the camera will be within the range offocus when the camera is set for sharp focus on van object 10 ft. away,and assuming that the focallength of the lens of the camera is 2 inches,

ring I6, on which scale A, the scale of object distances, is marked,will first be rotated until the graduation I6 of Vscale A is oppositethe mark 10. Plate I4 is next rotated,Y as by means of the knurled knob31 until theV center mark on the head of pointer arm 48 is opposite thegraduation 5 of scale A. The camera opening graduation (scale B on plateI4) opposite the 2 inch graduation on the focal length scale C (on ringportion I2a) now indicates the camera opening to use. This computationis illustrated in Figure 10, and reference to the camera opening or Bscale as shown in that figure shows that the :camera opening or stopnumber graduation 20 is opposite the? inch graduation on the focallength amasar scale, meaning that the aperture. identified on the cameraas F/ZO should be used.

2. For an example of another use of the com-A puting device assume thatit is desired to find the nearest and furthest distances which will bewithin the range of focus when a camera, equipped with a lens of 4 inchfocal length, and using the camera opening F/S, is sharply focused on anobject 20 ft. away. In order to solve this problem plate I4 is rotatedto bring number 8 of the camera opening scale B thereon opposite the 4inch graduation on the focal length scale C on ring portion l2a, as isillustrated in Figure ,9. Now rotate ring I6 until the 2G ft. graduationof scale A thereon is opposite the mark or line of reference 18. Thecenter lines on the heads of the pointers and 48 will then point to 38ft. and to 13 ft. 6 in., respectively, which are the nearest andfurthest distances within the range of focus.

3. As a third application of the computing' device assume that it isdesired to nd the lens focal length required to insure that an object 5ft. from the camera will be within the range of focus when the camera issharply focused on an object 10 ft. away, using camera opening F/ZO. Thesolution of this problem is similar to the first illustration givenabove, and is also illustrated by the relative position of scales B andC as shown in Figure 10. The proper lens focal length is found byrotating scale A until l@ on that scale is opposite the mark or line ofreference 1U. Plate l, is then rotated Until the center line on the headof pointer 46 points to the graduation 5 on the distance scale lA. Thegraduation on the lens focal length scale C which is opposite thegraduation 2!) on the camera opening scale indicates the proper focallength to use, and as is illustrated in Figure l0, the graduation on thefocal length scale opposite 20, of the camera opening scale is 2,showing that the proper lens to use is one having a focal length of 2inches.

Figure 8 has been included in the drawings to facilitate a completeunderstanding of the con. struction of my computer, and the problemswhich it is adapted to solve. Referring to Figure 8, assume, that lens Lrepresents a simple bi-convex lens,` and that the rays from an objectpoint O are sharply focused on the photographic film or plate P. It willbe observed that the rays from a more distant object point F come to afocus a 1.

Short. distance before the plate, and diverge again to form a circle ofconfusion of light on the plete. Similarly the rays from a nearer objectpoint N willl be intercepted by the film before comllgv to. a focus, andform a circle of confusion. llfn this circle of confusion is not toolarge, all objects within the circle will be reproduced on thefi1msubstantially info cus, TheA size of this circle QI U UIL: u!

Where D is, thediameter of the lensl aperture Q is.Y the diameter of thecircleof; confusion u' is the'distance of the sharply focused image fromthe lens, and

@fais the distance of the slightly blurred image from the lens.

This proportion may also be written From a fundamental lawof opticalimagery. Obj ect and image distances are related by the followingequation:

wat? also VTV? where u is the .distance of the object point O from thelens c is the distance of the object point N from the lens, and f is theequivalent focal length of the lens.

Making use of these relations, we obtain the object distance, c, interms of D, C, u, and f:

By an analagous line of reasoning, we can find that farthest objectdistance w beyond the object point O which will cause, a circle ofconfusion of diameter C. This object distance will be expressed by theequation a-ttf The computing device must solve the last two equations.The diameter D of the lens aperture can be determined from the speedindex or' F/number and the focal length of the lens, i. e.

Since it-has been assumedthatthe circle of confusion or blur circle inthe final picture will subtend an angle at the eye of approximately 3minutes of arc or less, which requires the diameter of C tobeapproximately 1/1000 of the focal length or less, the two computingequations can therefore be written The computing device is constructedto solve simultaneously both of these equations.

` Scalel C is calibrated in terms of log j. Since this scale cannotextend more than about. 160 of the entire' circumference of .the circledue to 75 the mechanical construction, the angular call` bratonvvasd'etermn'edby the factor 160 log f which allows a range of focal lengthsfrom 1" (1og.1=0) to 10 inches (log 10'=1.000). The calibrations weredivided equally on bothv sides of the vertical. Y

Scale B was similarlydetermined by the factor 160 log FV# (F/afi beingthe symbol for camera opening or stop number) and covers the range fromF /1.5 to F/32. Since log 1.5- .1'7609, and log 32=1.50515,the totalangular spread of the Ff# scale=l60 (150515-17609):212.65". 'Iherelative positions of scales B and C therefore gives us the divisionsince The total range of movement of the pointers 46 and 48 is fromabutting positions abutting the raised island 12 on which line 'l0 ismarked to positions approximately 180 apart. The maximum range from thenear to far object distances computed by the device is thereforedetermined by this range. If Weassume, as a practical limit, theshortest focal length (1) Will not be used at an F/ larger than F/ll,the maximum range in feet required can be determined by the twocomputing equations. Since the far distance v=, the object distance ucan be determined:

This means therefore that the calibration of the A or object distancescale, can be computed from the formula, Y

The entire range, Vfrom 2, ft. to infinity covers of the circumferenceof the range scale.

The calculation of the cam groove 60 will be determined by thecalibrations on the three scales, and by the dimensions of the pointerarms 46 and 48, and the curved arms B6 and 68 inside the mechanism. Inthe following calculations it is assumed that the physical dimensions ofthe space beneath the plate I4 permit a 90 movement of the pointers, andthat the dimension KL on the indicator arm (Figure 6') is approximately1/2 inch, and the dimension LM on the link is about .8 inch, Krepresenting the axis I8 of the pointers, L representing one of thepivots 61 or 69, and M representing the stud 64.

The position of indicator arms.46 and 48 is determined by means of thelink, and the posi- 8 tion ofthe point M. The location of M is in turnlocated by the cam groove 60,'and the guide slot 62. The cam groovetherefore must give the coordinate KM in accordance with the function Yf as determined by the relative positions of the B and C scales.Reference to Figure 6 shows that the relationship between the threepivotal points K, L and M, may be expressed,

KM=1/LM2-KL2 sin2 @-KL cos 0 Where KM is the radial coordinate of thecam groove, and 0 is the angle between either pointer 46 and 48 from theflxedvmark or reference line l0. We have previously found that 0 is afunction of the range u, which in turn is a function of the F/# and thefocal length. The dimension KM may be determined by substituting thedimensions of KL and LM in the above equation. For example, the radialdistance KM of the cam groove for a point corresponding to a setting ofl" (one inch) on the focal length scale and F/4.5 on the FV# scale wouldbe determined as follows:

1/xi ft.

u: 18.52 ft.

This requires an angle between pointers 46 and 48 Similarly, thedimension KM can be computed for each position of the B scale.

The computer described above may be a com-7 pact instrument of a size onthe order of the' light meters used by photographers. Being a separatedevice it is available for use in connec tion with any camera, and ithas the advantage that it is simple to operate and adapted to speedilysolve any of the various photographic problems referred to above. e

It will thus be seen that there has been provided by this invention anapparatus in which the various objects hereinabove set forth togetherwith many thoroughly practical advantages are successfully achieved. Asvarious possible embodiments might be made of the mechanical fea-I turesof the above invention and as the art herein described might be variedin Various parts, all without departing from the scope of the invention,it is to be understood that all matter hereinbefore set forth or shownin the accompanying drawings is to be interpreted as illustrative andnot in a limiting sense.

What I claim is:

1. A computing device for'determining for any camera the lens focallength to be used with a given camera opening to obtain a desired rangeof focus, or the camera opening to be employed to obtain a desired rangeof focus with a lens of given focal length, or the depth of focusobtainable with a lens of a given focal length using, a given cameraopening and whether an object' at a given distance will be Within therange of focus, which comprises, a base, a stud extending upwardly fromsaid base and adapted to serve as the axis for a number oi superimposedelements, a circular plate mounted for rotation around said stud andhaving thereon a scale of logarithmic calibrations of camera openings, aring rotatably mounted on said base concentrically with said plate andhaving thereon a scale of the reciprocals of object distances, said ringbeing spaced radially outwardly from said plate leaving an annular spacetherebetween, another ring fixed on said base within said space having asemi-annular` portion of substantially the full height of said space,and a semi-annular portion only partially filling said space verticallyand so leaving a space above it between said plate and said ring, saidportion of full height having thereon a scale of logarithmiccadibrations of lens focal lengths, a guide slot in said base, a camgroove cut in the under face of said plate, a stud having its lower endslidably enaged in the said guide slot and having its upper endslideably engaged in said cam slot and serving as a cam iollower, a pairof pointer arms rotatably mounted on said axial stud, a plurality ofcurved and oppositely positioned arms each pivoted at one end on saidcam follower stud, and each pivotally connected at its other end to oneof said pointer arms respectively, intermediate its ends, said camgroove being disposed relative to said guide slot so that movement ofthe plate or the pointer arms causes movement of said cam follower studwith resulting and proportionate movement of the pointer arms or theplate.

2. A photographers computing device for determining any one of the threevariables of lens focal length, camera opening, and depth of focus, whenthe other two of said variables are known, comprising, a segment of aring having thereon a scale of logarithmic calibrations of lens focallengths, a circular plate having thereon a scale of logarithmiccalibrations of camera openings, and a ring having thereon a scale ofthe reciprocals of object distances, said members being coaxiallymounted and disposed with said segment between said plate and said ringthus leaving a semi-annular space between said plate and said ringbeyond the extremities of said segment, said segment being stationaryand said plate and ring rotatable, and a pair of pointers mountedcoaxially with said members for rotative movement toward or away fromone another, said pointers each comprising a head portion adapted to iitinto and travel in the said semi-annular space between said plate andsaid ring, said plate having a cam groove cut in one face thereof, abase member having a guide slot, and a stud one end of which isslideably engaged in said guide slot and the other end of which isslideably enu gaged in said cam slot, and a pair of links pivotallyconnected between said stud and said pointer arms respectively, said camgroove serving when said plate is rotat-ed to control the position oithe pointer arms to cause them to assume positions corresponding tofunctions of camera openings and lens focal lengths.

3. A photographers computing device for deftermining any one of thethree variables or" lens focal length, camera opening, and depth offocus, when the other two of said variables are known, comprising, asegment of a ring having thereon a scale of logarithmic calibrations oflens focal lengths, a circular plato having thereon a scale oflogarithmic calibrations of camera openings, and a ring having thereon ascale of the reciprocals of object distances, said members beingcoaxially mounted and disposed with said segment between said plate andsaid ring thus leaving a semi-annular space between said plate and saidring beyond the extremities of said segment, said segment beingstationary and said plate and ring rotatable, `and a pair of pointersmounted ooaxially with said members for rotative movement toward or awayfrom one another, said pointers each comprising a head portion adaptedto lit into and travel in the said semi-annular space between said plateand said ring, said plate having a cam groove out in one face thereof, abase member having a guide slot, and a stud one end oi which isslideably engaged in said guide slot and the other end of which isslideably engaged in said cam slot, and a pair of links pivotallyconnected between said stud and said pointer arms respectively, said camgroove serving when said pointer arms are directly moved to control theextent of resulting rotation of said plate so that the depth of focusindicated on the scale of object distances by the spread of the pointerarms is a function of the camera openings and lens focal lengthsindicated by opposed graduations on said camera opening and lens focallength scales.

WILLIAM M. FBAZER.

No references cited.

